Unveiling the Potential of Room-Temperature Synthesis of a Mixed-Linker Zeolitic Imidazolate Framework-76 for CO2 Capture

A room-temperature synthesis was used to prepare ZIF-76 by combining the organic linker imidazole and 5-chlorobenzimidazole, with the addition of NaOH as a modulator. The synthesis process was optimized by modifying the existing method, which includes the introduction of heating, different types of solvent, and adjustment to the reactant ratio. The synthesized MOFs were characterized to evaluate their crystallinity, textural properties and surface morphology. The result demonstrated that the introduction of heat led to the formation of ZnO whereas the replacement of DEF-DMF with methanol resulted in the production of amorphous material. Moreover, a change in precursor ratio led to the production of ZIF-76 with a low yield and surface area. Meanwhile, CO2 adsorption was performed in a pressure range of 0-1.2 bar at 298.15 K. Notably, ZIF-76B with a low surface area exhibited a greater CO2 uptake capacity of 1.43 mmol/g compared to ZIF-76A, which recorded 1.29 mmol/g. Furthermore, the isotherm and kinetic models were applied to fit the experimental CO2 adsorption data. The analysis of the adsorption models indicated that the CO2 adsorption was primarily governed by a monolayer formation on a homogeneous surface. Nevertheless, there was a slight diversion in terms of predicted qm with experimental data, which could be attributed to the adsorption not yet reaching equilibrium. Additionally, the kinetic model was applied to the initial stage of adsorption in the pressure range of 0-0.24 bar. The Elovich model was found to fit better with the CO2 uptake capacity data of ZIF-76A and ZIF-76B suggesting that the adsorption process may involve multiple mechanisms.